An existing monitor support device, which can be clamped on a tabletop, includes an upright frame, a slide unit disposed on a rear surface of the upright frame and slidable upward and downward along the rear surface of the upright frame, a monitor mount disposed on a front surface of the upright frame and slidable upward and downward along the front surface of the upright frame, a work platform disposed below the monitor mount, and a clamping seat disposed on the slide unit opposite to the upright frame and configured to clamp on the tabletop. The slide unit includes an air pressure bar, and a slide member that is slidable upward and downward along the upright frame through the air pressure bar. Through relative sliding movement of the upright frame and the slide unit, the height of the monitor mount and the work platform relative to the tabletop can be adjusted according to the requirement. Although the use of the air pressure bar to control the height adjustment has a high accuracy, the price of the air pressure bar is expensive, so that the manufacturing cost of the existing monitor support device is high. Further, because the work platform is fixed to a bottom end of the upright frame and cannot be rotated or folded, the work platform occupies a substantial space when not in use.